This invention relates to virtual storage systems, and more specifically to storage virtualization controllers for multi-tier storage systems with low latency cache and backup power sources.
In certain storage systems multiple logical storage devices of varying capacity and capability are connected to a storage virtualization appliance that is configured to automatically manage the movement of data between the logical storage devices. Storage virtualization appliances have access to high speed, low latency cache memory, so that frequently accessed information in the storage system can benefit from low latency. The low latency cache memory is comprised of volatile memory, which needs backup power to ensure that information contained in the cache memory is not lost in the event of power failure. Backup power sources have limited power, such that once a power failure is detected the contents of the volatile memory cache must be transferred or de-staged to nonvolatile logical storage devices quickly in order to avoid information loss. Backup power limitations can reduce the useable limits of cache memory, since the cache size must be small enough to be de-staged before the backup power depletes, which in turn limits the performance of the overall storage system.
The prior art does not provide adequate means to de-stage data from the volatile memory cache to nonvolatile cache in the event of power failure. Additionally, the prior art fails to provide adequate mechanisms for distinguishing between a de-stage triggered by cache loading and a de-stage triggered by power interruption. Prior art systems also have limited or no signaling between storage system elements, such as the backup power sources and other elements used for managing data movement between logical storage devices.